The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Internal combustion engine vehicles that employ automatic transmissions typically include a torque converter positioned between the engine and the transmission of the vehicle. A torque converter is a fluid coupling device typically including an impeller coupled to an output shaft of the engine and a turbine coupled to the input shaft of the transmission. The torque converter uses hydraulic fluid to transfer rotational energy from the impeller to the turbine. Thus, the torque converter can disengage the engine crank shaft from the transmission input shaft during vehicle idling conditions to enable the vehicle to stop and/or to shift gears.
The rotational speed of the impeller relative to the turbine in the torque converter is typically different so that there is a converter slip therebetween. Because large slips between the engine output and the transmission input significantly affect the fuel economy of the vehicle, some vehicles employ a torque converter clutch (TCC) for controlling or reducing the slip between the engine and the transmission. The TCC can also mechanically lock the impeller at the output of the engine to the turbine at the input of the transmission so that the engine and transmission rotate at the same speed. Locking the impeller to the turbine is generally only used in limited circumstances because of various implications.
Thus, a TCC generally has three modes. A fully locked mode as just described, a fully released mode and a controlled slip mode. When the TCC is fully released, the slip between the impeller and the turbine of the torque converter is only controlled by the hydraulic fluid therebetween. In the slip mode, the slip between the torque converter impeller and turbine is set so that it does not exceed a predetermine amount by controlling the pressure of the hydraulic fluid in the TCC.
In a torque converter with a TCC in slip mode, changes in conditions affecting the torque converter can cause increases or reductions in slip. For example, a change in engine torque can change the slip in the torque converter before commands to the TCC, including a time lag between the change in slip and reactions in the TCC to control the slip, can control the slip back to a desired or target value. As a result, transitions in the torque converter can generate unintentional changes to the slip. For example, an unintended reduction in slip to a low or zero slip resulting in a torque converter crash can result from an unintended reduction in slip. Crashes cause perceptible changes to the operation of the vehicle or cause drivability issues. Quick and accurate detection of a torque converter crash can be helpful to minimize adverse effects of the crash.